United Kingdom - Passport & Nationality - British Citizenship by Double Descent (SA Stateless Child)
A child born outside of South Africa to South African parents during the period up to 7 December 2010 had to be registered as a South African in order to become a South African citizen. In other words, the child did not automatically become South African at birth. What this meant is that, if their country of birth did not confer citizenship on the child at birth, the child would have been born stateless - that is, without a nationality.
Where one of the parents was a British citizen, then it is possible to register the child as a British citizen as long as this happens before they turn 18. It does not matter that child subsequently acquired a nationality - for example, if the parents subsequently registered the child as a South African.